Structural and biochemical features distinguish the foot-and-mouth diseasevirus leader proteinase from other papain-like enzymes

The structures of the two leader protease (L-pro) variants of foot-and-mout h disease virus known to date were solved using crystals in which molecules were organized as molecular fibers. Such crystals diffract to a resolution of only approximately 3 Angstrom. This singular, pseudo-polymeric organiza tion is present in a new L-pro crystal form showing a cubic packing. As mol ecular fiber formation appeared unrelated to crystallization conditions, we mutated the reactive cysteine 133 residue, which makes a disulfide bridge between adjacent monomers in the fibers, to serine. None of the intermolecu lar contacts found in the molecular fibers was present in crystals of this variant. Analysis of this L-pro structure, refined at 1.9 Angstrom resoluti on, enables a detailed definition of the active center of the enzyme, inclu ding the solvent organization. Assay of L-pro activity on a fluorescent hex apeptide substrate showed that L-pro, in contrast to papain, was highly sen sitive to increases in the cation concentration and was active only across a narrow pH range. Examination of the L-pro structure revealed that three a spartate residues near the active site, not present in papain-like enzymes, are probably responsible for these properties. (C) 2000 Academic Press.